In case you’ve not read how the Bloom Box system works, each “power plant-in-a-box” come chock full of thin fuel cells, bundled and packaged into an outdoor-safe case. The individual cells soak up oxygen on one side, “and fuel on the other. The two combine within the cell to create a chemical reaction that produces electricity,” reported CBS last night. “There’s no need for burning or combustion” but it still requires some form of fuel to work. What kind is up to the owner.

“Our system can use fossil fuels like natural gas. Our system can use renewable fuels like landfill gas, bio-gas,” Sridhar says. “We can use solar.”

In some cases, CO2 is still being emitted by whatever power is feeding the Bloom Box. Rather than calling this new device “zero emission energy,” maybe it’s better to think of it as a booster pack for already-green sources and as an impressive new filter for dirty ones.

Mr. Sridhar said the Bloom Energy Server has been generating electricity at a cost of 8 to 10 cents a kilowatt-hour.

In California, where Bloom has installed 30 fuel-cell systems, commercial electricity rates averaged about 14 cents a kilowatt-hour in October 2009, according to the latest figures from the United States Department of Energy. Elsewhere, commercial rates averaged 7 to 24 cents a kilowatt-hour.

Last July, eBay flipped the switch on five Bloom Energy Servers that now supply 15 percent of the electricity at its San Jose, Calif., campus, or about five times as much energy as generated by its 3,248 solar panels, according to Amy Skoczlas Cole, director of the company’s Green Team.

“We’re expecting a three-year payback period,” said Ms. Skoczlas Cole, adding that the calculation includes state and federal tax incentives that halved the price of the fuel cells.